DINOMYID&CA VIID& 489 



Ccelogenys. 1 This genus is readily characterised by the presence 

 of five hind toes, and the extraordinary development of its zygo- 

 matic arches, which are enormously expanded vertically, forming 

 great convex bony capsules on the sides of the face, enclosing 

 on each side a large cavity lined with mucous membrane, and 

 communicating by a small opening with the mouth. The Paca 

 C. paca) is about 2 feet long, and, like the species of Dasyprocta, lives 

 generally in the forests or along the banks of rivers. This species 

 appears to date from the epoch of the Pleistocene deposits of the 

 Brazilian caves. A smaller species from Ecuador, living at ele- 

 vations of from 6000 to 10,000 feet, has been described as 

 C. taczanowskii. 



Family DINOMYID^E. 



Distinguished from the Dasyproctidce by the cleft upper lip, 

 rather long and bushy tail, the presence of four digits in both fore 

 and hind feet, and the complete clavicles. The manubrium is 

 broad ; the optic foramina are confluent ; the incisors broad ; and 

 the molars rootless, with enamel-folds dividing them into transverse 

 laminae. 



Dinomys. 2 The sole representative of this family is the Rodent 

 known as D. branicki, of which hitherto only a single specimen has 

 been obtained. This was captured in Peru, where it was found at 

 daybreak walking about a courtyard ; the inhabitants of the dis- 

 trict were previously unacquainted with the species, from which 

 its extreme rarity may be inferred. Externally it resembles much 

 the Paca, having similar S-like nostrils ; but in the laminated 

 molars, and many features of the skeleton, it differs from all the 

 other Rodents with hoof-like nails. It is regarded by its describer, 

 the late Professor Peters, as a connecting link between the 

 Octodontidce, Chinchillidce, Dasyproctidce, and Caviidce. 



Family CAVIID^E. 



Terrestrial or natatorial forms, with short incisors, strong man- 

 dibular masseteric ridges, long and curved paroccipitals, and palate 

 contracted in front. Fore feet with four digits, hind feet with 

 three. Clavicles imperfect. Molars divided by enamel-folds into 

 transverse laminae ; milk-teeth shed before birth. Other characters 

 as in Dasyproctida>. Neotropical region. 



Cavia. s Limbs and ears short, subequal ; tail none. Vertebrae : 

 C 7, D 1 3, L 6, S 4, C 7. This genus includes several species widely 



1 F. Cuvier, Ann. du Musium, vol. x. p. 203 (1807). 



2 Peters, Monatsber. Ak. Berlin, 1873, p. 551. 



3 Pallas, Misc. Zool. p. 30 (1766) ; ex Klein. 



